homework problems (galvanometers)

[eku_girl83]

I figured out the capacitor/charging problem that I last posted. Here's my latest cause of worry:
1)The Resistance of the coil of a pivoted-coil galvanometer is 7.92 Ohms and a current of .0194 A causes it to deflect full scale. We want to convert this gavanometer to an ammeter reading 10 A full scale. The only shung available has a resistance of .0436 Ohms. What resistance R must be connected in series with the coil?

I used the equation (Ifs)(Rc)=(Ia-Ifs)Rsh, where Ifs = .0194, Rc=7.92 Ohms, Ia=10 A. I then solved for Rsh and subtracted .0436 (the shunt available) from it. Why do I not get the correct answer?

2) A 150 V voltmeter has a resistance of 15000 Ohms. When connected in series with a large resistance R across a 105 V line, the meter reads 57 V. Find the resistance R.

Any help would be appreciated...Thanks!

[turin]

Originally posted by eku_girl83
1) ...
Why do I not get the correct answer?Sorry, I don't follow the question very well. From where did you get that equation?

OK, I gave it a closer look. You seem to be forgetting about what the question wants you to find. Hint #1: how many resistances should you be dealing with? Hint #2: where does the unknown resistance go? Hint #3: your equation needs just a slight modification.




Originally posted by eku_girl83
2) ...
Find the resistance R.This is a voltage divider. Use the voltage divider formular.